Short radius, fibre, pipe bend



Sept. 5, 1961 F. B. BURNS ETAL 2,998,985

SHORT RADIUS, FIBRE, PIPE BEND Filed May 2, 1958 2 Sheets-Sheet 1WEA'AIWEUMM? I HEAT F SGU/QCE Z4 Fredrick 5. Burns fdward M. JbhnsonINVENTORS.

flttarn ey P 5, 961 F. B. BURNS ETAL 2,998,985

SHORT RADIUS, FIBRE, PIPE BEND Filed May 2, 1958 2 Sheets-Sheet 2Fredrick 6. Burns fdwam M. Jfirzson INVENTORS.

BY Q ya United States Patent 2,998,985 SHORT RADIUS, FIBRE, PIPE BENDFredrick B. Burns, West Allis, and Edward M. Johnson,

Oak Creek, Wis., assignors to McGraw-Edison Company, Milwaukee, Wis., acorporation of Delaware Filed May 2, 1958, Ser. No. 732,704 2 Claims.(Cl. 285-179) This invention relates in general to a short radius,fibre, pipe bend and also to a method and apparatus for forming suchshort radius fibre bends adapted to later impregnation with a suitablesaturant such as coal tar pitch and the like.

In recent years there has been a tremendous expansion in the use oftubular conduit and pipe formed of pulp fibre. In straight stock length,the material is well adapted to fast production by mass productiontechniques and when saturated with a suitable saturant such as coal tarpitch and the like, has good durability and use.

Much of the manufacture of various shaped components has heretofore beendone by hand operation. Various shaped components have also been madefrom other materials. Utilization of these components in ap plicationsgoverned by installation and material codes has been in some casesrefused in the interests of uniformity in the overall installation.Therefore, for purposes of uniformity, a pitch-fibre short radius elbowis very desirable. Further, even in hand operations, it has been veryditficult to produce so-called short radius fibre bends due to theinherent characteristics of the wet tubes. One mass production techniquefor production of the short radius bends involves the use of containermeans for the containment of both the inner and outer surfaces of thetube during the manufacture process, this being undesirable in that manyhand operations in opening and closing the outer container means areinvolved.

It is an object of the invention to provide as an article ofmanufacture, a short radius, fibre, pipe bend having regularly spacedcompression crease marks on the inner side of the bend to therebyprovide a more uniform and superior product as contrasted with a bendhaving random crease marks.

It is a further object of this invention to provide a new and bettermethod and apparatus for the production of short radius bends.

Another object of this invention is to provide apparatus of the typeaforementioned for forming short radius bends from elongated preformedwet tubes of fibrous material without requiring container means toprevent radial expansion of the bends during the manufacture thereof.

A further object of the invention is to provide an apparatus and methodof the aforedescribed type wherein parallel spaced compressiveindentations are made on the outer periphery of the wet tube such thatin making the short radius bend, the indentations become compressioncrease marks on the finished product.

A further object of the invention is to provide a method and apparatusfor manufacturing short radius fibre bends which is easy to operate,easy to manufacture and maintain and is otherwise well adapted for thepurposes for which it was designed.

The novel features that are characteristic of this invention are setforth with particularity in the appended claims. The invention itself,however, both as to its organization and its method of operation,together with additional objects and advantages thereof will best beunderstood by the following description of specific em- Patented Sept.5, 1961 Ice bodiments when read in connection with the accompanyingdrawings in which:

FIG. 1 is a front plan view, partially in section, of a preformed wetelongated tube;

FIG. 2A is a view similar to FIG. 1 showing the tube undergoing aprestressing operation;

FIG. 2B is a sectional view along the lines 23 of FIG. 2A;

FIG. 2C is a sectional view similar to FIG. 2B showing the extent anddepth of the indentation of the prestressing operation;

FIG. 3 is a fragmentary front plan view, a portion of which is insection, similar to FIG. 2A showing an alternative method ofprestressing;

FIG. 4 is a semidiagrammatic view, a major portion of which is insection, of apparatus operable to form a short radius fibre bend;

FIG. 5 is a fragmentary sectional view of the apparatus in FIG. 4 at adifferent stage of the operation;

FIG. 6 is a semidiagrarnmatic view of another step in the manufacturingoperation showing the short radius bend still on a portion of themandrel and disposed in a drying oven;

FIG. 7 is a semidiagrammatic view of another step in the manufacturingoperation showing the impregnation of the raw short radius fibre bends;and

FIG. 8 is a front view of the finished short radius fibre bends, thedotted portions showing stock that was removed in the finishingoperation.

In the manufacture of short radius fibre bends, an elongate tube 10 maybe formed of cellulose material on a standard forming machine and aplurality of laminates is convolutely rolled to a wall thickness whichis standard for the straight stock pipe or conduit for which thefinished product is to be associated. Thetube after being rolled becomessubstantially a seamless homogeneous mass wherein the interlaminar bondsapproach the intralaminar bonds. The water content of this wet fibroustube 10 is preferably that of the normal value made on the formingmachine for use in the manufacture of straight stock fibre pipe orconduit. (It is to be noted that it is of considerable value to use astandard tube as a starting point for the short radius bends as thisdoes not require a modification of existent production machinery ortechniques.)

As shown in FIGS. 2A and 2B the wet tube 10 may be cut to appropriatelength and subjected to a prestressing operation. The prestressingcomprises the placing of indentations 11 at spaced parallel intervalsalong a portion of the outer periphery of the tube 10. The identationsmay be formed by a suitable meap s such as a roller 12 which engages theinside of the pipe to provide a support for a roller .13 having enlargedindenting mea'ns 13a associated therewith. The indentations 11 areplaced on the outer periphery of the tube 10 and are generally normal tothe axis of the tube and preferably extend only around 290 of theperiphery. The 70 of the outer periphery represented by referencenumeral 14 is preferredly not subjected to the prestressing operation.

As shown in FIG. 2A, the indentations 11 are, for example, placed atapproximately 0.750 inch intervals along the outside of the tube. Thespacing selected is desirable; for example, for a bend having a 7"radius to the inner surface of the bent tube. .An example of the depthand width of the indentations 11 is to stress a A inch deep, inch widemark along the periphery. The above example dimensions are preferreddimensions for a four inch wet pipe made according to industry standardshaving a wet wall thickness of approximately 0.430 inch, the normalwater content of the pipe being approximately 76 percent by weight. Itis to be palis applied to one end of the tube.

ticularly noted that while this prestressing process is being describedrelative to 4 inch pipe, the concept of course has equal application topipe and conduit of all sizes, although the precise dimensions, depthand spacings aforementioned may vary as per the size of the unit underconsideration.

An alternative to the above prestressing operation is shown in FIG. 3 ofthe drawings, the inner prestressed indentations 11 being preferablyoffset relative to the outer indentations 11 and are placed on the tubeby the roller 12 having enlarged marking means 12a spaced therealong.The spacings between the indentations 11' are preferably the same asthat between indentations 11; however, they are offset approximately0.375 inch /2 the distance) with respect to the outside indentations 11.

While the means for forming the proper indentations 11 for prestressingthe elongated wet fibre tube is shown as separate and discreteapparatus, it is, of course, apparcut that the prestressing operationmay be conveniently accomplished while the tube 10 is disposed on theforming apparatus 16 shown in FIGS. 4 and 5. This is particularly trueof the preferred prestressing operation shown in FIGS. 2A, 2B and 2C,i.e., outside prestressing only.

Turning now to the bending operation, apparatus 16 is operable to formthe tube 10 into the raw bend 33 shown in FIG. 5. More particularly, thebending apparatus 16 comprises three major components, i.e., the mandrelmeans, the tube mover means 30 and the tube freeing means. Moreparticularly, the mandrel means comprises first, second and thirdportions, the first portion 18 being substantially a straight cylinder,the second portion 19 being a curved portion detachably connected to thefirst portion and the third portion 20 which has substantially the sameradius of curvature as portion 19 and is detachably connected thereto.As shown in section, the interior of the mandrel means may be hollow andhas closure means 25 and 24 disposed respectively in the first portion13 and at the junction of portions 19 and 20 to define a chamber 21.Heat source means is attached by a suitable conduit 26 to the interiorof the helical spring 28 which in turn engages the tube engaging portion29 which is here shown in the form of an annular ring. It is to be notedthat a number of other mechanisms can be used to provide the function ofthe drive mechanism 30.

In the bending operation the Wet prestressed tube is loaded onto thestraight portion 18 of the mandrel means when portions 19 and 2%) areremoved therefrom. A garter or tube protector 31 is placed on the frontor leading end of the tube 15 to prevent splitting thereof. Next theportions 19 and are attached to portion 18 and the driving member 27,which may be attached to an air cylinder not shown, is actuated. Theforce of the driving member 27 is transmitted to the tube engagingmember 29 by the spring 23 which serves both as a force transmittingmember and flexible drive means for pushing the tube 15 around thecurvatures 19 and 20.

The normal tendency for the wet tube after loading same onto mandrel 18is to adhere thereto. This characteristic is greatly heightened when acompressive force In order to free the prestressed tube 15 for movementalong the mandrel portions 18 and 19, the heat source means is activatedso as to supply a sudden hot jet of heat to enclosure or chamber 21 onthe mandrels 18 and 19 to create a cushion of steam between the interiorsurface of the tube 15 and the exterior surfaces of the mandrel portions18 and 19. Once the heat is admitted to the enclosure 21 suilicient toelevate the temperature to the desired level, the drive mechanism 30must be actuated very quickly to prevent drying out and scorching of theprestressed tube 15.

Experimentally, it has been determined that the most beneficial resultsare obtained with an enclosure 21 temperature sufiicient to produce atemperature, measured at the surface of the mandrels 18 and 19, abovethe boiling point of water. It is, of course, obvious that the mandrelmay be heated by any suitable means and even may be disposed in an ovenor the like for preheating thereof if desired.

After actuation of the drive mechanism 30, the tube 15 is pushed in apath such that it ends up on the detachable third mandrel portion 20.This mandrel portion 20 is preferably the exact curvature desired forthe final radius of the bend and is cool since end wall 23 preventssubstantial heat transfer thereto. The coolness of mandrel 20 alsofacilitates easy handling of the now bent tube 33 and mandrel portion20.

The third mandrel portion 20 having the bend 33 disposed thereon is thendetached from portion 19 and this assembly is then placed in a dryingoven 32 (shown in FIG. 6). This assembly is then dried according tostandard procedures, the particular temperatures and air movementsrequired being determined according to conventional techniques.

After removal from the drying oven the dried bent tube 33 is removedfrom the mandrel portion 20 and is then disposed in a suitableimpregnation tank 35 having coal tar pitch 34 therein all of which isshown semidiagrammatically in FIG. 7. The actual impregnation is alsodone according to conventional techniques, i.e., a combination of heatedpitch, vacuum and pressure to assure complete and thorough impregnation.After removal of the now impregnated bend 33 from the impregnation tank35, the bend is quenched in a conventional manner to congeal the coaltar pitch saturant 34. The bend is then subjected to a machiningoperation whereby the end portions 37 and 38 are removed and tapers 39and 40 are formed at the ends of the segments for cooperation with otherfittings as suitable and desired. Of course, other types of connectionmeans, such as screw threads or the like, may be machined on the ends ifdesired. It is to be observed that the amount of stock 37 and 38 whichis shown removed from the bend 33 is to be considered semidiagrammaticrather than a precise dimensioning.

It will be noted that during the forming or bending operation, theprestressed creases or indentations 11 on the tube 15 becomescompression crease marks 11' in both the fibre bend 33 and in thefinished article 36. These crease marks 11 are, of course, no longer ina parallel relationship to each other. Rather, they are in alignmentwith the radii of the toroidal segment shape assumed by the bend in thebending and drying operations.

It will be further noted that the prestressed tube 15 was disposed onthe mandrel 18 such that are segment 14 was at the top of the apparatusso that when the driving mechanism was actuated, the larger diameter ofthe toroidal shape would not have any compression crease marks thereon.Stated another way, the compression crease marks 11' are disposed onlyon the small radius side of the curved mandrel since this is where thecompression forces exist. In this regard, it has been found that shortradius bends may be made without prestressing operation. However, a muchmore uniform product both in strength and in appearance, is obtained bythe prestressing operation. This obtains because the preselection of thepoints of stress provides less failure of interlaminar bonds which isoccasioned by random stressing. The random stressing operation causesthe weakest point to become weaker and since the break down ofinterlaminar bond is in many respects similar to a puncture typeconcept, random stressing provides many more rejects. The weakening ofthe weaker point will cause many more failures in a random stressed bendrather than in a prestressed bend.

It should be pointed out that the method and apparatus above describedshifts the neutral axis from the center line of the tube to the outerside thereof during the bending operation. In most bending operationsthe center line of a tube is a neutral axis. This causes material belowthis axis to be in compression and material above this axis to be intension. In fact the outer surface is actually stretched. Fibrousmaterial cannot be stretched to any appreciable degree without tearing.In the instant method, most all of the forces in the bend arecompressive forces due to shifting the neutral axis to the outer radius.The bending is, therefore, accomplished essentially through compressionand it is particularly important that a minimum of disturbance be doneto the fibrous inner structure of the tube wall to prevent weakeningthereof. The prestressing operation together with the driving of thetube from the rear end thereof are particularly advantageous in thisregard. It should also be noted that the speed of the drive mechanism isimportant. It must be fast enough so that tearing of the top surface ofthe tube does not occur. It is not exactly known why a slow drive willtear the upper surface. However, experiments show that speed of movementof the drive mechanism is essential to operation.

Although a specific method and embodiment have been shown and described,it is with full awareness that many modifications thereof are possible.The invention, therefore, is not to be restricted except insofar as isnecessitated by the prior art and by the spirit of the appended claims.

What is claimed as the invention is:

1. As an article of manufacture, a short radius, fibre, pipe bend formedfrom a straight section of fibre pipe,

the material of the pipe having the ability to densify when wet, andhaving generally the shape of a segment of a toroid; said pipe bendbeing formed of a plurality of layers of cellulose fibre material whichare held together by interlaminar fibre bonds, said fibre material beingimpregnated with a hardenable waterproofing material; said pipe bendfurther having a plurality of evenly spaced grooves formed in thesurface thereof along the inner side of said bend, each of said groovescomprising a recess pressed into the surface of said pipe before bendingthereof to thereby prestress and densify said fibres for a portion ofthe thickness of said pipe, each of said recesses having a depth of lessthan the thickness of said pipe, and a length of at least half of theperiphery thereof and extending for a uniform distance from each side ofthe line forming the shortest arc of curvature of said bend, whereby theaxis of bending of said pipe is beyond the midpoint thereof; said pipebend further having a plurality of radially directed compressioncreases, each of said creases coinciding with one of said grooves, saidpipe having a substantially smooth interior and exterior surface, saidgrooves and the resultant densified portions controlling the compressivestresses Within the Wall of the pipe on the inner side of the bend tominimize weakening of the interlaminar bonds and to maintain anunimpeded internal flow dimension within the pipe.

2. A short radius, fibre, pipe bend as set forth in claim 1, wherein thesaid grooves are formed on the internal and external surfaces of saidpipe bend, said internal grooves being staggered relative to saidexternal grooves.

References Cited in the file of this patent UNITED STATES PATENTS540,584 Dieckmann June 4, 1895 1,877,628 Replogle Sept. 13, 19321,880,053 Schur et a1. Sept. 27, 1932 2,057,916 Quartz Oct. 20, 10362,327,347 Gibbin Aug. 24, 1943 2,465,257 Nebesar Mar. 22, 1949 2,706,497Shobert Apr. 19, 1955

